The present invention relates to coverings for architectural openings, and, more specifically, to horizontal blinds, such as Venetian blinds, designed to selectively tilt open or tilt closed portions of the blind.
Typically, a Venetian blind has a top head rail or other frame member, which both supports the blind and hides the mechanisms used to raise and lower or open and close the blind. The raising and lowering is done by a lift cord attached to the bottom rail (or bottom slat). The slats, which are supported from the head rail, may be allowed to tilt so as to open the blind to allow a maximum of light through the blind, or to close the blind with the room side down (the edge of the slats which is closest to the room is facing down, which means that the other edge of the slats, the edge which is closest to the window or the wall, will be facing up), or to close the blind with the room side up.
Tilting the blind closed may be done for the purpose of blocking out light, or for obtaining privacy, or both. In order to obtain the optimum performance from the blind, it may be desirable to open one portion of the blind while closing another portion of the blind. For instance, it may be desirable, in an office setting, to tilt closed the lower portion of the blind in order to block the glare of sunlight on a computer screen, or to provide privacy so someone standing outside the window cannot stare through the window and see what is on going on inside the room. However, at the same time, it may be desirable to have the upper portion of the blind tilted open to allow some natural light and/or ventilation into the room. Another instance of an application for such a “split” blind design may be in a home where the floor of the house is at a higher elevation than the ground outside. A person standing in the house could freely see outside, but a person from the outside could not effectively see inside except for the uppermost reaches as allowed by the open section of the blind.
In addition to the issue of privacy and glare elimination, the light control feature of the split blind design is also beneficial in that it minimizes the ultraviolet light deterioration resulting from sunlight impacting on interior furnishings, rugs, hardwood floors, etc. while still maintaining indirect lighting from the outside as well as a clear view of the outside. This is particularly practical and applicable in buildings with a roof overhang over the window area or where the windows are recessed into the wall, creating an overhang.
Japanese Patent Application Number S63-55595 shows a design in which one portion of the blind can be closed while another is open. This reference seems to require at least 450 degrees of rotation of the tilt rod to complete one entire cycle, from one extreme position to the other extreme position of the blinds. There are two sets of tilt cords per tilt station, with the first set of tilt cords attached to a drive drum portion and the second set of tilt cords attached to a driven drum portion. The drive drum must rotate a full 360 degrees before it engages the driven drum, and it must then rotate an additional amount (probably no less than an additional 90 degrees and possibly another 360 degrees) to actuate the second set of tilt cords attached to the driven drum. By then, the first tilt cords are wrapping over themselves onto the drive drum, resulting in a shortening of these tilt cords, which raises the bottom rail away from the window sill, causing an undesirable daylight gap at the bottom of the blind. The overwrapping also may cause a problem with the cords tangling. In addition, the drive drum must rotate a full 360 degrees once it reverses direction before it can engage the driven drum in the opposite direction.